1. Field of the Invention
The present invention relates to the packaging of electronic devices in general and in particular the packaging of said devices to provide protection against electromagnetic radiation.
2. Prior Art
There are many applications where it is desirable to provide electromagnetic radiation shielding which protects a device from externally generated radiation and prevents the device from radiating into the surrounding environment. Examples of such applications are data processing systems including personal computers and point of sale terminals. In describing the preferred embodiment for practicing the present invention, a point of sale terminal will be used as the example. However, it should be understood that the principal packaging technique and advantages are applicable to other devices.
In most countries the amount of radiation that a device can emit is regulated. A few companies have even set their own standards regarding radiation emission. In some cases the companies impose regulations even more stringent than the regulations of some countries. Thus, the problem arises as to the manner in which these regulations can be met.
It is well known in the art that electromagnetic emission can be controlled by encasing equipment in a conductive enclosure. Gaskets are used to control leakage from areas between two surfaces. Examples of this well-known technique are given in U.S. Pat. Nos. 4,396,795; 4,399,316; 4,322,572; 4,381,421 and 3,594,490.
In addition to the radiation problem, manufacturers are being asked to provide users with relatively low cost and reliable data processing devices. The cost of purchasing and operating a data processing device tends to increase if a customer engineer has to visit the customer location to install or correct a problem on the data processing device. To alleviate this cost problem, the prior art adopts the so-called Field Replaceable Unit (FRU) concept. The concept is one of modular design and packaging. Whenever a system goes down, the user identifies the defective FRU and replaces it with one that is not defective. The defective FRU is returned to the manufacturer or a designated repair center. There it is repaired and can be returned to a customer for reuse. Thus, when a machine problem occurs, a customer can correct the problem without using the services of the customer engineer.
In the past the above-identified problems have been treated as separate and independent problems. Neither the manufacturers nor the packaging industry have provided a satisfactory solution to either problem. As a result designs that optimize the solution for the customer maintenance problem do not adequately satisfy the radiation control problem and vice versa. Moreover, the prior art solutions require special tools and possibly some mechanical know-how since in most cases the covers of the machine must be removed so that one can gain access to the components inside the machine. Once the covers are removed, unless they are carefully replaced, usually by trained personnel, there is a high probability that the electromagnetic shielding is adversely affected.